EWPAA Structural Plywood and LVL Design Manual - Engineered ...

• prefabricated housing for walls, floors and roofs;• folded plate roofs;• curved roofs for domestic, commercial and industrial buildings;• concrete formwork• a range of applications dependent upon the designers ingenuity.11.4 Stressed Skin Panel Design – Panel ActionSimplistically, the flat panel with plywood skins rigidly fixed to either side of timber stringers, performsstructurally as a series of composite I-beams. The plywood skins develop most of the normal stress dueto bending of the panel whilst the shear stresses are taken by the stringers.Shear LagA stress resultant phenomena resulting from loading thin walled structures, and to which the elementaryflexure theory does not directly apply due to the influence of shear deformations, is termed shear lag.The normal stress distribution across the flange of a stressed skin panel subjected to bending is nonuniformas shown in FIGURE 11.2.FIGURE 11.2: Distribution of flange stressesTherefore, to apply the simple flexure formula to this non-uniform stress distribution requires using areduced or effective flange width (b e ) rather than the actual width (2b). This reduced width can beevaluated if the stress distribution shown in FIGURE 11.2 by the broken lines is known. To determine b e thenbecomes a matter of making the area of the rectangle defined by the solid lines equal to the area of theactual stress distribution.North American approach is to use the basic spacing (b) shown in FIGURE 11.3 as the design parameter.144